Low-interference seeker dome attachment

ABSTRACT

Attachment means for positioning a dome upon the airframe of a guided missile. An attachment ring is chemically bonded to the interior of a glass dome. The attachment ring has interior threads which match exterior threads on the steel airframe of the missile. The ring is made of a low thermal expansion alloy. The thread interface has a pitch angle of Beta . As the threads of the airframe move with respect to the threads of the attachment ring due to thermal expansion or contraction the movement will be parallel to the thread face. This parallel motion will induce only frictional forces across the thread interface causing negligible stresses in the ring and airframe.

United States Patent n 1 Jacobson 1 1 Sept. 11, 1973 [54] LOW-INTERFERENCE SEEKER DOME 3,427,977 2/l969 Mott lO2/lO5 ATTACHMENT 2,997,595 8/1961 Cary et al. 244/3.l6 3,165,749 1/1965 Cushner 244/316 [75] Inventor: Michael D. Jacobson, Ridgecrest,

Calm Primary Examiner-Benjamin A. Borchelt [73] Assignee: The United States of America as Assist! 'f"; Tudor represented by he secretary of the Attorney-R. S. Scrascta et al. Navy, Washington, DC. 57 A TRA T [22] Filed: Feb. 28, 1972 l 1 1 Attachment means for posmonmga dome upon the air- PP- 229,840 frame of a guided missile. An attachment ring is chemically bonded to the interior of a glass dome. The at- 52 us. (:1. 102/702 R 343/872 has hheads which mamh 51 Int. Cl. "11 01 1 42 hheads 1 the airframe missile- The 58 Field of Search 102/702 105 79 ring is made a The 102/56. 285/390 0 thread interface has a pitch angle of B. As the threads of the airframe move with respect to the threads of the [56] Reierences cued attachment ring due to thermal expansion or contraction the movement will be parallel to the thread face. UNITED STATES PATENTS This parallel motion will induce only frictional forces :F at igs-5 g across the thread interface causing negligible stresses in aines 3,064,578 11/1962 Henderson et al. the mg and a'rframe' 3,027,842 3/ 1962 Hopkins 102/702 P 5 Claims, 3 Drawing Figures Patented Sept. 11, 1973 3 $1100 Ls-Shoet 2 g ZAA Fig. 2

Patented Sept. 11, 1973 3,757,698

3 Sheets-Sheet 3 LOW-INTERFERENCE SEEKER DOME ATTACHMENT BACKGROUND OF THE INVENTION 1. Field of the Invention This invention pertains to means for attaching an optical dome to the airframe of a guided missile.

2. Description of the Prior Art The problem of attaching a glass optical dome to the metallic body of a guided missile arises from two basic differences in the characteristics of glass and metal. The first and probably most important characteristic is that of the coefficients of thermal expansion. Metals generally have higher coefficients of thermal expansion than glasses. The second characteristic is that of thermal conductivity. Metals have relatively high thermal conductivity while the thermal conductivity of glass is relatively low. Under conditions of rapid temperature increase at the external surfaces of a radome or nose cone, as occurs in flight due to aerodynamic heating effects, it is found that the cylindrical metal portion within the axial bore of the glass body may become hotter than the surrounding glass walls because of the differing thermal conductivity characteristics. As a result of the higher thermal conductivity and expansion, the cylindrical metal portion expands radially much more and faster than the surrounding glass wall. Thus, a substantially rigid bonding layer affords no allowance for this differential expansion and this produces a severe stress in the thin surrounding glass wall resulting in fracture or bursting of the glass body.

There are many methods of missile dome attachment; however, few of them utilize a technique of compensating for differing thermal expansion of the dome and airframe. The joints that allow for the difference in expansion are quite complex or cannot maintain dome position with respect to the airframe center line.

This invention compensates for differing thermal expansion rates of the dome and airframe and also keeps the dome position on the missile center line.

SUMMARY OF THE INVENTION This invention provides structure for attaching a glass dome to the airframe of a guided missile. Three primary parts are involved: the dome, the missile airframe and an attachment ring. The circular attachment ring is chemically bonded to the dome on the interior of the dome near the truncated portion. The attachment ring has internal threads while the airframe has matching external threads. The threads have a pitch angle B equal to the arctan of Z /R where Z equals the average distance of the edge of the airframe thread from the dome seat on the airframe and parallel to the airframe axis and R equals'the radial distance of the same thread edge from the axis of the airframe. By selecting the pitch angle to be this value, the thread interface between the cone thread and airframe thread will be subject to frictional forces only as the airframe expands or contracts and moves with respect to the dome.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an exploded view of the invention;

FIG. 2 is a cross sectional view taken in the direction of arrows 22 of FIG. 1; and

FIG. 3 is a cross sectional view of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Optical dome 10 made of Coming 79l3 glass is attached to steel airframe 12 via attachment ring 14 made of a very low thermal expansion alloy such as Unispan 36. Hermatic gasket 16 serves to prevent air or moisture from passing through the small space between attachment ring 14 and airframe 12. The threads on both the attachment ring and airframe have a pitch angle of B. This particular pitch angle allows the threads to move parallel to the thread interface as the threads move with respect to one another. This movement will occur due to the greater thermal expansion characteristics of the steel airframe with respect to the attachment ring. If the metal of the glass-to-metal joint were hotter than the glass, the metal would expand more than the glass even if the expansion rates were the same. This makes it desirable to protect the metal portion of the joints from the hot air stream. Thus, the threads are separated from the surface of the airframe by the length of wall 18 plus some.

Thepitch angle B is the key to the above design. If B is correctly chosen, the radial position of the dome can be maintained and the rapidly expanding steel airframe will not stress the dome. In the determination of B it is necessary to consider the movement of thread 20 of the airframe. The change in the movement of thread 20 is a function of Z and R. This can be expressed by the formula lel to the thread surface and, therefore, produce no radial force (i.e., dome stresses). A changing pitch angle is impractical; therefore, the average pitch angle will be used.

Bum TAN-l ena ave) where R, R 2.9 in

Z Z Z in and B TAN" (0.30/29) 59 This pitch angle is optimized only for the middle thread; therefore, in operation, the threads closer to the dome seat than the middle thread will tighten and those farther from the dome seat than the middle thread will loosen-This characteristic will have negligible effects in most cases. The pitch angle will also provide for obtaining radial positioning of the dome when the dome is screwed on.

It can be assumed that the R and Z coordinates of the ring are equal to the R and Z coordinates of the airframe. If the thread faces that are in contact are cut at the angle B determined by the R and Z coordinates of the thread, the difference in thermal expansion will result in motion parallel to the thread face. This parallel motion will induce only frictional forces across the thread interface, causing negligible stresses in the ring and airframe.

What is claimed is: 1. A nose cone in combination with the air frame of a guided missile comprising:

threads on said frame; threads on said cone; said threads meshing with one another; the interface of said threads being at a pitch angle of B whereby thermal expansion will result in motion parallel to said interface; said angle {3 being equal to arctan (Z /R where Z equals the average distance of the edge of said frame thread from the dome seat on said frame and parallel to said axis and R equals the radial distance of said frame thread edge from said axis.

2. The combination of claim 1 wherein said cone threads are on an attachment ring which is secured to said cone.

3. The combination of claim 2 wherein said ring is located on the interior of said cone whereby said ring is isolated from the air stream to lessen the thermaleffects on said ring.

4. The combination of claim 2 wherein said ring is attached to said cone by a chemical bond.

5. The combination of claim 2 wherein said ring is made of a low thermal expansion alloy. 

1. A nose cone in combination with the air frame of a guided missile comprising: threads on said frame; threads on said cone; said threads meshing with one another; the interface of said threads being at a pitch angle of Beta whereby thermal expansion will result in motion parallel to said interface; said angle Beta being equal to arctan (Zavg/Ravg) where Zavg equals the average distance of the edge of said frame thread from the dome seat on said frame and parallel to said axis and Ravg equals the radial distance of said frame thread edge from said axis.
 2. The combination of claim 1 wherein said cone threads are on an attachment ring which is secured to said cone.
 3. The combination of claim 2 wherein said ring is located on the interior of said cone whereby said ring is isolated from the air stream to lessen the thermal effects on said ring.
 4. The combination of claim 2 wherein said ring is attached to said cone by a chemical bond.
 5. The combination of claim 2 wherein said ring is made of a low thermal expansion alloy. 